Dual fuel engines are well known in the art and combust a mixture of two different types of fuel. For example, a particular dual fuel engine can combust a mixture of a liquid fuel (e.g., diesel fuel) and a gaseous fuel (e.g., natural gas). By combusting two different types of fuel, advantages of both fuels (e.g., efficiency, power, emissions, cost, etc.) can be realized.
In order to properly control performance of a dual fuel engine, the pressures and/or flow rates of the two different fuels into the engine should be tightly regulated. Historically, the pressures and/or flow rates of the fuels have been regulated independently, for example by way of a variable displacement liquid fuel pump and by way of a gas vent. The variable displacement liquid fuel pump, however, may be too expensive and/or complex for some applications. In addition, venting of the gaseous fuel may be undesirable due to the harm such gaseous fuel may cause to the environment and because such venting may be wasteful. Finally, it may be desirable to link the pressures and/or flow rates of the two fuels in some operations, such that desired ratios of the fuels may be provided.
One way to control the pressures and flows of a dual fuel system is described in U.S. Pat. No. 6,298,833 issued to Douville et al. on Oct. 9, 2001 (the '833 patent). In particular, the '833 patent describes a system for delivering diesel fuel and gaseous fuel through an injector into an engine. The system employs a pressure balancing device having a first chamber in fluid communication with a supply of the diesel fuel and with the injector, a second chamber isolated from the first chamber and in fluid communication with a supply of the gaseous fuel and the injector, and a piston separating the first and second chambers. The piston is movable to maintain a pressure of the diesel fuel a fixed amount higher than a pressure of the gaseous fuel. In addition, a position of the piston is sensed and used to control a diesel fuel pump, thereby maintaining the pressures of both the diesel fuel and the gaseous fuel within a desired range.
While the system of the '833 patent may adequately control diesel and gaseous fuel pressures for some applications, it may still be less than optimal. In particular, the system may not allow for independent control of diesel and gaseous fuel pressures. Additionally, in order to maintain the pressure of the gaseous fuel below that of the diesel fuel, the system of the '833 patent may vent natural gas to atmosphere in certain operating conditions. These deficiencies may reduce the overall efficiency of the system, and may be harmful to the environment.
The exemplary embodiments of the present disclosure are directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.